1. Field of the Invention
The present invention concerns konjak food gelled by a vegetable juice and a process for producing such konjak food.
2. Description of the Prior Art
Konjak is a sort of jelly like foods and it has been traditionally produced from konjak tubers by slicing dry tubers into thin chips, grinding the chips into a refined konjak flour, dispersing the thus obtained flour into water and adding an alkaline chemical such as calcium hydroxide to the dispersion, which is then heated and subsequently allowed to cool, to form an aqueous konjak gel.
The konjak gel obtained is almost tasteless and has a translucent milky color. Regarding it composition, it contains a great amount of fibrous substances (so-called dietary fibers) and has been stressed by dietitians nowadays as low caloric and health-keeping food.
As described above, since konjak is tasteless and has a dull color appearance it is in sharp contrast with the attractive presentation widely sought and enhanced in new products in compliance with contemporary nutrition feelings and tastes. Therefore, konjak is not so favored as ordinary food but its use is rather limited as an additive to foods and beverages with dietetic qualities and purposes.
A further handicap in the commercialization of konjak originates from the odor of the konjak gel. Whereas the konjak itself has no substantial specific odor, its releases a peculiar unappealing odor after gelation with calcium hydroxide (lime).
It may be considered to reduce the amount of calcium hydroxide added. However, this attempt is very limited due to the risk of affecting the gelification process itself. About 0.4% by weight of calcium hydroxide (about 0.2% by weight converted as Ca) based on water present in the final gel is necessary for obtaining a satisfactory gel and, if it is reduced, for example, by about 25%, commercially acceptable konjak food can be produced no more.
In my prior patent application, directed to the production of tofu and like other soybean food and now allowed as U.S. Pat. No. 4,992,291, I have succeeded in replacing magnesium chloride used so far as a gelling agent with a liquid extract from vegetable leaves.
However, it could not be expected that my discovery mentioned above regarding the production of tofu be applicable to the production of konjak gel because of the following reasons.
The production processes for tofu seems to be similar to that of konjak since a gelation step by an alkaline chemical is conducted for each of them. However, gelation takes place for bean protein by using magnesium chloride in the case of tofu. On the other hand, konjak glucomannan (a sort of polysaccharides) is at first hydrolyzed into glucose and mannose by calcium hydroxide which are then coagulated by crosslinking and complex reactions under a catalytic effect of calcium. Accordingly, mechanisms of chemical reactions are quite different between them.
In addition, gelling conditions for konjak are much more delicate then those for tofu. Indeed, preparation of konjak actually fails sometimes even in a traditional process using lime and they say that this is mainly attributable to accidental inclusion of a trace amount of impurities such as starch, salt, etc. during the production process.
Therefore, I was rather negative to use a vegetable juice as a substitute for a gelling chemical in the production of konjak because the vegetable juice contains various known and unknown substances which would give undesired effects on the gelling process.